NORD Drivesystems BU0050 - Manual (Page 68)

NORD USS and Modbus RTU Manual
68 Subject to technical amendments BU 0050 GB-3111
2.6 Exception Responses
If a query by the Modbus Master cannot be answered correctly, an error message is sent instead of the normal
response. The error message is structured as follows:
Slave

Master
Function Code 1 Byte 0x80 + Function code of the Master query
Exception Code 1 Byte 0x01 to 0x06
Exception Code Description
01h

A function code has been sent, which is not supported by the FI.
02h

The telegram which has been sent is too long.

For read queries, the data range to be read out is too large.

The queried parameter is not known.

The parameter sub-index is not known.
03h

An incorrect data content has been transmitted in the function "Write Single Coil".

The number of parameters is above the limit set by Modbus.
04h

Error in access to the parameter database of the FI.

The number of coils to be written in the function "Write Single Coil" has been
exceeded
06h

The Slave is still occupied with current query and cannot receive a new order.
Example:
Parameter P102, parameter set 2 is written with the value 0x0123.
Query (Master

Slave) Response (Slave

Master)
Address 0x08 Address 0x08
Function Code 0x06 Function Code 0x06
Address High 0x19 Address High 0x19
Address Low 0x81 Address Low 0x81
Parameter value High 0x01 Parameter value High 0x01
Parameter value Low 0x23 Parameter value Low 0x23
CRC High 0x9E CRC High 0x9E
CRC Low 0x6E CRC Low 0x6E
2.7 Watchdog
Modbus communication can be monitored via the parameter P513. Monitoring is started with the first valid
telegram. If the FI does not receive a new telegram within the time set in P513, error 10.0 is triggered in the FI.